In the grass, the mice start to reproduce. They reproduce multiple times within the group to create a variety of different mice.
When the mice reproduce, they overproduce at first. Eventually most of these mice die because of selection.
You can see variation in the mice because of their color. There are white, grey, and brown mice. The white mice do not blend in as well as the other two colors, making them easily spotted by predators. The variation helps the species to adapt to the environment.
You can see that the brown and grey colored mice have survived. The brown mice are able to blend in with the tan/brown color of the dirt. Half of the grey mice are able to survive by blending in with rocks. The others were too visible and were eaten by predators.
A hawk nearby can see the white mice very clearly. He specifically preys on them because they are easiest to see and do not blend in. He takes some grey mice and white mice back to a tree to eat.
The mice have now adapted to their environment. They are all now brown mice. They adapted to a brown color so their predator can not see them, causing them to live longer so they can continue to reproduce. The white mice have been killed off along with the grey mice because they could not survive long in the conditions they were in.